The present invention relates to a heating appliance, comprising a burner of the type having full premixing and forced draught, and having a mixing chamber to which an air supply line and a fuel supply are connected, said mixing chamber having a burner plate which is provided with apertures and which adjoins a combustion chamber in which a heat exchanger is disposed some distance from the burner plate and is passed through by a medium to be heated, a flue being connected to said combustion chamber.
Such a heating appliance is known, for example, from Dutch Patent Application 7906458. Such burners work with a certain gas/air mix ratio to obtain good combustion with the highest possible output. In order to adapt the heat production to the heat demand, the quantity of gas is varied, so that the quantity of air supplied also has to be varied to obtain the desired mix ratio. The problem occurring with such a modulating control is that at a minimum load on the heating appliance, i.e. when little fuel and consequently little combustion air are supplied, the heat transfer surface of the heat exchanger is relatively large compared with the quantity of flue gases flowing past it through the heating appliance. The result of this is that at minimum load the flue gases are greatly cooled, even to below dew point, so that condensation will occur. If the design is not suitable for condensation, or if the condensation cannot be discharged because the appliance is fitted at a place which is unsuitable for this the occurrence of condensation is an undesirable phenomenon which must be avoided.